The invention relates to a semicircular radial antenna having a wide-angle beam used within the range of GHz to tens of GHz.
A horn antenna has generally been known as an antenna for radiating, in the form of a beam, a radio wave within the range of GHz to tens of GHz. Since the horn antenna has a narrow angle of horizontal radiation, consideration has recently been given to a semicircular radial antenna having a wide-angle beam radiation characteristic.
The semicircular radial antenna comprises a semicircular upper waveguide plate and a semicircular lower waveguide plate. The waveguide plates are spaced a predetermined distance from each other so as to oppose each other. Base portions (i.e., linear edges) of the waveguide plates are short-circuited by a short-circuit wall, thereby constituting a semicircular radial waveguide between the upper and lower waveguide plates. Power is externally fed to the semicircular radial waveguide. Such an antenna can achieve a wide-angle beam characteristic such that half width is about 120°.
As mentioned above, the semicircular radial antenna achieves a wide-angle beam characteristic. However, there has not been considered the relationship among the structure of semicircular antenna, the horizontal beam width and the orientation of a radiated vertical beam. In addition, improvements in gains thereof are further expected.
In recent years, a radio wave in a GHz band is used in many cases in a communication system such as a satellite broadcast, a GPS, a mobile terminal, an ETC (Electronic Toll Collection) system, etc. For example, a 2.5 GHz band is used in the satellite broadcast and a 2 GHz band is used in the mobile terminal. Further, a 1.5 GHz band is used in the GPS and a 5 GHz band is used in the ETC. Further, the arriving direction of the radio wave in the satellite broadcast and the GPS is the zenithal direction. The arriving direction of the radio wave in the mobile terminal is the horizontal direction. Accordingly, these arriving directions are different from each other. Therefore, the radio wave as an object is conventionally received by using a dedicated antenna with respect to each communication system.
In this situation, it is necessary to arrange plural kinds of antennas when plural communication systems are utilized. It is complicated to arrange the plural kinds of antennas in this way, and the required area to arrange the antennas is increased. Accordingly, it is desired to receive the radio wave by a single kind of antenna in the plural communication systems. However, when the radio wave of each communication system is received by a single kind of antenna, since the arriving directions of the radio wave are different from each other as described the above, it was difficult to practically use the antenna since multidirectivity was required.